Field
At least one example embodiment relates to a method and/or an apparatus for diagnosing plasma in a plasma space. More particularly, at least one example embodiment relates to a method and/or an apparatus for diagnosing plasma, capable of diagnosing the spatial distribution of plasma in a plasma process chamber by using floating probes.
Discussion of the Related Art
Among the various devices used to fabricate semiconductor devices, a plasma device is widely used to form plasma inside a sealed process chamber maintained in a vacuum state, and to inject reactive gas into the chamber to deposit a thin film on a wafer or etch the thin film formed on the wafer. The plasma device may be applied to various fields because the process may be performed at a low temperature in which impurities in an impurity region formed in the wafer are not diffused. Plasma devices are also used for forming a thin film having a superior uniformity of thickness on a wafer with a large diameter. Plasma devices are also useful for achieving etch uniformity throughout the whole wafer when a thin film is etched. A Langmuir probe has been extensively used as a device capable of analyzing characteristics of plasma, namely ion and electron distribution, by measuring parameters of the plasma in the plasma device. The Langmuir probe employs a floating probe in order to measure the electron temperature and the ion density of plasma.
The floating probe is connected to a plasma medium through a capacitor to cut off a DC component of current generated by the floating probe, which minimizes an influence exerted on the plasma medium by the probe such that plasma potentials are static and electrically float. Accordingly, ion density and electron temperature of the plasma are calculated from probe current having an AC component without the DC component. In general, the electron density in an apparatus for diagnosing plasma is derived from the ion density because the electron density is not easily calculated. Because the ion density is equal to the electron density in positive plasma, the calculation of the electron density for positive plasma is not required. However, because the ion density is expressed as the sum of a negative ion density and an electron density for negative plasma, the calculation of the electron density is desired to more accurately diagnose the plasma characteristics.